The present invention relates generally to a method of magnetically recording predetermined information signals on a magnetic recording medium used in a magnetic recording/reproducing device.
Recently, a magnetic recording/reproducing device has been increasing in recording density in order to achieve a small size and large capacity. Especially, in the field of a hard disk drive used as a typical magnetic memory, apparatuses with an areal recording density of more than ten gigabits per square inch (15.5 Mbits/mm2) are already available on the market. Practical use of memories with an areal recording density of 20 gigabits per square inch (31.0 Mbits/mm2) has been discussed. Thus, the technique in this field has been progressing rapidly.
One of the technical features that has enabled such high recording density is the increasing linear recording density due to the improvements of a medium performance and a head-disk interface performance, and the advent of a new signal processing method such as xe2x80x9cpartial responsexe2x80x9d. Recently, however, the rate of increase in track density exceeds that of linear recording density greatly, which is a primary factor for the increase in areal recording density. The practical use of a magneto-resistive type head, which is superior to a conventional inductive type magnetic head in reproduction-amplitude performance by far, has contributed to the increase in track density and has enabled the reproduction of signals from a track whose width is a few microns or less, with a high S/N ratio. It is expected that the track pitch will reach the sub micron range in the near future along with further improvement of the head performance.
In order that a head scans such narrow tracks correctly to reproduce signals with a high S/N ratio, a technique of tracking servo of the head plays an important role. A hard disk drive to which such a tracking servo technique is applied has areas (hereafter referred to as xe2x80x9cpreformatxe2x80x9d) where a tracking servo signal, an address data signal, and a reproduction clock signal are recorded at predetermined angles over the circumference of a disk, that is, over 360 degrees. The magnetic head reproduces such signals every predetermined interval, so that the magnetic head can scan a track correctly while the head position is verified and corrected.
A tracking servo signal, an address data signal, and a reproduction clock signal are to be reference signals for the magnetic head to scan a track correctly. Therefore, precise positioning accuracy is required in recording the signals. In a conventional hard disk drive, a disk is incorporated into the drive, and then using a special servo recording apparatus, preformat recording is carried out with a magnetic head whose position is controlled precisely.
In the preformat recording of a servo signal, an address data signal, a reproduction clock signal, and the like using a magnetic head as described above, there have been problems as follows.
First, the recording using a magnetic head is basically linear recording utilizing the relative movement between the magnetic head and a magnetic recording medium, and therefore, in the above-mentioned method of recording using the special servo recording apparatus while the magnetic head position is controlled precisely, preformat recording takes a long time and the servo recording apparatus is quite expensive, thus increasing the cost.
Second, there is a problem in that due to the spacing between a magnetic head and a recording medium and diffusion of the recording magnetic field caused by the shape of a pole provided in the magnetic head, magnetization at the track edges of the recorded preformat signals lacks steepness in transition. In a current tracking servo technique, a head position is detected based on a change amount of reproduction amplitude when the magnetic head deviates from a track to be scanned. Therefore, it is required not only that the head scans a track correctly with a high S/N ratio as in reproducing data signals recorded in an area between servo areas, but also that in a signal track formed by the preformat recording, the magnitude of reproduction amplitude is steeply changed when the magnetic head deviates from a track to be scanned, i.e. the off-track characteristic is steep. The above-mentioned problems go against these requirements and make it difficult to carry out the precise tracking servo technique in the submicron track recording expected in the future.
In order to solve the aforementioned problems in the conventional preformat recording using a magnetic head, the following method has been disclosed.
For instance, JP 10-40544 A discloses the following method. That is, magnetic portions of a ferromagnetic material are formed on a substrate in a pattern corresponding to information signals, which then is used as a master information carrier. The surface of the master information carrier is brought into contact with a surface of a sheet-like or disc-shaped magnetic recording medium on which a ferromagnetic film or a ferromagnetic powder coating layer is formed, and a predetermined magnetic field is applied. Then, the magnetized pattern corresponding to the information signals formed in the master information carrier is recorded into a magnetic recording medium.
In the method disclosed in JP 10-40544 A, with a recording magnetic field generated from the ferromagnetic film on the surface of the master information carrier magnetized in one direction, a magnetized pattern corresponding to the ferromagnetic film pattern in the master information carrier is transfer-recorded into the magnetic recording medium. In other words, a ferromagnetic film pattern corresponding to a tracking servo signal, an address data signal, a reproduction clock signal, or the like is formed on the surface of the master information carrier by photolithography or the like, so that preformat corresponding to the pattern can be recorded on the magnetic recording medium.
The conventional recording with a magnetic head is basically a dynamic track recording based on the relative movement between the head and a medium. On the contrary, the method described above is characterized by a static area recording without being accompanied by relative movement between the master information carrier and a medium. With such a characteristic, the technique disclosed in JP 10-40544 A can provide the following quite useful effects with respect to the aforementioned problems in a preformat recording.
First, since the areal recording is employed, a significantly shorter time is required for the preformat recording as compared to that in a conventional recording method using a magnetic head. In addition, the expensive servo recording apparatus for carrying out recording while the magnetic head position is controlled precisely is not required. Consequently, the productivity in the preformat recording can be increased considerably and the production cost can be reduced.
Second, since the static recording is carried out without being accompanied by relative movement between the master information carrier and a medium, the surface of the master information carrier and the surface of a magnetic recording medium can be brought into close contact with each other, thus minimizing the spacing between the both in recording. Furthermore, since no diffusion of the recording magnetic field due to the shape of a pole provided in the magnetic head is caused, magnetization at the track edges of the recorded preformat signals has excellent steepness in transition compared to the case of recording with a conventional magnetic head, thus achieving more accurate tracking.
In the recording of information signals using such a magnetic transfer technique, an arranged pattern corresponding to information signals provided in a master information carrier is transfer-recorded into a magnetic recording medium as a magnetized pattern at one time. Therefore, it is important that high density information signals are recorded uniformly and stably throughout the whole area of the magnetic recording medium.
The present invention is intended to record high density information signals uniformly and stably in a magnetic recording medium, particularly a disc-shaped magnetic recording medium such as a fixed hard disk medium, a removable hard disk medium, a large capacity flexible medium, or the like, with high productivity in a short time.
A method of recording magnetically on a magnetic recording medium of the present invention is based on a method in which using a master information carrier with an arranged pattern formed of magnetic portions of a ferromagnetic film on a substrate in a shape corresponding to predetermined information signals, the master information carrier is superposed on a magnetic recording medium with the magnetic portions facing the magnetic recording medium and the magnetic portions of the master information carrier are magnetized with a magnetizing head, thus transfer-recording the arranged pattern formed in the master information carrier into the magnetic recording medium as a magnetized pattern. In order to solve the above-mentioned problems, the magnetizing head includes an annular magnetic circuit with a gap, and a strength of a magnetic field applied to the master information carrier by magnetic flux leaking from portions other than the gap is set to be 20% or less of that of a magnetic field applied to the master information carrier by magnetic flux leaking from the gap. According to the present invention with this basic structure, signal information in an arranged pattern provided in the master information carrier can be transfer-recorded throughout the magnetic recording medium as signal information in a magnetized pattern uniformly and stably without causing deterioration in signal quality.
In the method with the above-mentioned structure, preferably, prior to the transfer-recording using the master information carrier, a magnetic field for direct current erasing is applied to the magnetic recording medium with a magnetizing head to magnetize the magnetic recording medium in one direction, then the master information carrier is superposed on the magnetic recording medium magnetized in the one direction, and a magnetic field in an opposite direction to that of the magnetic field for direct current erasing is applied to the magnetic portions of the master information carrier with the magnetizing head, thus transfer-recording the arranged pattern formed in the master information carrier into the magnetic recording medium as a magnetized pattern.
In the above-mentioned method, the magnetizing head includes a first magnetic core half and a second magnetic core half, the first magnetic core half and the second magnetic core half oppose each other to form an annular magnetic circuit with a gap, and the magnetizing head is designed to have one of the following shapes so that a strength of a magnetic field applied to the master information carrier by magnetic flux leaking from portions other than the gap is suppressed to be 20% or less of that of a magnetic field applied to the master information carrier by magnetic flux leaking from the gap.
That is, an outer periphery in a cross-section parallel to an annular magnetic path of the magnetic circuit has a substantially polygonal shape in which at least vertexes adjacent to the gap have a curved shape with a curvature of a radius of at least 0.5 mm.
Alternatively, an outer periphery in a cross-section parallel to an annular magnetic path of the magnetic circuit may have a substantially polygonal shape in which at least vertexes adjacent to the gap have an interior angle of at least 100 degrees.
Alternatively, an outer periphery in a cross-section parallel to an annular magnetic path of the magnetic circuit may have a substantially polygonal shape with a supposed vertex positioned on a center line of the gap in the vicinity of the gap and the supposed vertex has an internal angle in a range between 100 and 170 degrees. The sides adjacent to the supposed vertex on the center line of the gap in the magnetizing head may have an outwardly curved shape.
Alternatively, an outer periphery in a cross-section parallel to an annular magnetic path of the magnetic circuit may have a substantially elliptical shape with no vertex.
In the aforementioned configuration, at least one of the first magnetic core half and the second magnetic core half of the magnetizing head may be formed of a permanent magnet. Alternatively, the first magnetic core half and the second magnetic core half of the magnetizing head may be positioned to oppose each other while sandwiching a permanent magnet therebetween. Alternatively, a coil for direct current excitation may be provided around at least one of the first magnetic core half and the second magnetic core half of the magnetizing head.
A magnetic recording/reproducing device can be provided, which includes a magnetic recording medium that has been subjected to preformat recording using the method according to the above-mentioned configuration.
Moreover, a hard disk drive also can be provided, which includes a disc-shaped magnetic recording medium incorporated therein, in which a magnetized pattern of predetermined information signals has been transfer-recorded into a magnetic film using the method with the above-mentioned configuration.